Wood-type golf club heads generally have a mass in the range of about 150-250 g. A portion of this mass sustains the structural integrity of the club head. The remaining mass, referred to as “discretionary” mass, may be strategically distributed to improve the head's mass properties and/or inertial characteristics.
Known methods of increasing the available discretionary mass, e.g. reducing the thickness of the club head walls, produce minimum benefits. Accordingly, the capacity of modern wood-type club heads to deliver improved performance is qualified, in part, by the amount of discretionary mass attainable through conventional methods.
Generally, golfers have a natural tendency to strike the golf ball about the face center of the club head. The face center, in most wood-type clubs, is the point on the club face where maximum face rebound occurs at ball impact and is also known as the Coefficient of Restitution (COR) “hot spot”. Although ball impact at the COR “hot spot” yields maximum face rebound, it may produce inaccurate shots because, in conventional club heads, the “sweet spot” (the orthogonal projection of the head's center of gravity (CG) onto the striking surface of the head and the point on the club face where no head rotation or gear effect occurs) is generally located above the COR “hot spot”. Hence, for conventional wood-type clubs, only a single performance variable, i.e., either maximum face rebound associated with ball impact about the COR “hot spot” or shot accuracy associated with ball impact about the “sweet spot”, may be augmented for any one golf shot.
Generally, ball impact about the face center of a conventional wood-type club exaggerates both the head rotation and gear effect of the club head, causing a loss of carry distance and accuracy.
Shot accuracy and distance are also affected by the depth of the CG relative to the club face. In conventional drivers, the CG is typically positioned near the face. Shallow CG placement decreases dynamic flexing of the shaft toward alignment with the CG, thus decreasing the beneficial lofting of the head and the closing of the face at impact with the ball. Additionally, a shallow CG decreases the radius of rotation of the face on off-center hits, thus decreasing shot accuracy.